Alcoholism and alcohol abuse are complicating factors in most chronic medical and psychiatric illnesses. Alcohol physiological dependence and associated withdrawal episodes are thought to constitute a powerful motivational force that perpetuates continued alcohol use/abuse and contributes to relapse. In humans, the identification of genes that influence alcohol physiological dependence and withdrawal has been extremely limited. Thus, the use of preclinical (animal) models of alcohol physiological dependence that closely approximate the clinical situation is essential to elucidate the gene networks involved. We have used these methods to identify a gene (Mpdz) involved in alcohol withdrawal in mice that is now being studied in populations of human alcoholics by NIH-NIAAA intramural scientists. Quantitative trait loci (QTLs) are chromosome sites containing alleles (genes) that influence a quantitative (complex) trait such as predisposition to alcohol physiological dependence and associated withdrawal. Previously, we confirmed QTLs on chromosomes (Chr) 1, 4, and 11 that jointly have a major influence on alcohol withdrawal in mice. This proposal is focused on the Chr 4 QTL with proven effects on acute and chronic ethanol withdrawal. During the current funding period, we fine mapped this QTL to a 1.8 Mb (<1 cM) interval (syntenic with human Chr 9p24-p22.3) and identified Mpdz (which encodes the multiple PDZ domain protein, MPDZ or MUPP1) as a quantitative trait gene (QTG) for alcohol withdrawal. Using a congenic strain that isolates this locus on an inbred genetic background as well as novel Mpdz transgenic animal models, we propose to continue toward elucidation of the mechanism by which Mpdz affects alcohol withdrawal. We propose the following three aims: (1) Using viral mediated gene transfer and/or RNA interference approaches, rigorously test the hypothesis that Mpdz expression in circuitry implicated in ethanol withdrawal in fact influences withdrawal severity. Pharmacological manipulation in discrete brain regions will provide mechanistic information about MPDZ and its influence on ethanol withdrawal. (2) Use neurochemical and neurophysiological analyses to provide mechanistic answers to identify a signal transduction pathway influenced by MPDZ. (3) Using congenic and Mpdz transgenic animal models, test Mpdz's role in behavioral responses to ethanol (i.e., acceptance drinking, conditioned taste aversion, ataxia sensitivity, and tolerance) that are genetically correlated with Mpdz status and expression, as well as other CNS hyperexcitability states. An innovative feature of this proposal is to combine robust behavioral models of alcohol withdrawal with state-of-the-art strategies to elucidate Mpdz's mechanism of action. MPDZ is thought to regulate 5HT2C and GABAB receptor function. Given the growing body of evidence that dysregulation of GABA and serotonin transmission contributes to alcoholism, we expect that our results will inform developing models and facilitate progress in human alcohol genetics by setting the stage for future translational and mechanistic studies. We have already established that a gene, Mpdz, substantially influences genetic risk for alcohol physiological dependence and associated withdrawal episodes in mice. This proposal is focused on explaining the mechanism by which Mpdz affects alcohol withdrawal, as well as determining its influence on other behavioral responses to alcohol. Given that Mpdz encodes a protein that regulates the function of serotonin and GABA receptors in the brain, and dysregulation of serotonin and GABA function contributes to alcoholism, we expect that the results of this research will facilitate progress in the treatment of alcohol dependence.